The present invention relates to nonwoven fabrics having a multilayer structure and a method of producing the same. More particularly, the present invention relates to an improvement in a nonwoven fabric comprising a surface substantially smooth, an upper layer having high density and a lower layer having low density, and in a method of producing such fabric.
A nonwoven fabric of the type comprising a surface substantially smooth, an upper layer having high density and a lower layer having low density is used generally as an outer cover member of body exudates treatment articles, such as sanitary napkins, disposable diapers and the like. This type of nonwoven fabric, however, is not in a satisfactory degree in its capability preferably required as said outer cover member, that is, in smoothness, touch and strength of its surface; in bulkiness and cushion of entire structure, particularly in its lower layer, when in wetted state; and in surface permeability of body exudate when it is in a state of being in contact with the body exudate.
The present invention is not necessarily limited to a nonwoven fabric to be employed as an outer cover member of said body exudates treatment article and a method of producing such nonwoven fabric. It is to be understood, that the invention primarily aims at providing a nonwoven fabric which is preferable to dissolve the disadvantages seen in the prior art described above, and an improvement in a method of producing such nonwoven fabric.
A principal object of the present invention is to provide an arrangement to obtain a nonwoven fabric which is excellent in smoothness, touch and strength of its upper layer surface, wherein the arrangement comprises the step of distributing fibers with a relatively fine denier and a relatively large amount of adhesive bonding materials onto the upper layer of the nonwoven fabric, and a method of producing such nonwoven fabric.
Another object of the present invention is to provide an arrangement to obtain a nonwoven fabric which is excellent in bulkiness and cushion in its entire structure, particularly in its lower layer, and such excellency does not fall even in wetted state, wherein the arrangement comprises the step of distributing fibers with a relatively coarse denier, a relatively small amount of adhesive bonding materials, and a preferable amount of hydrophobic fibers onto the lower layer of the nonwoven fabric, and a method of producing such nonwoven fabric.
Still another object of the present invention is to provide an arrangement to obtain a nonwoven fabric which is superior in permeability and in preventing back flow of body exudates against the nonwoven fabric and which can maintain dryness in the surface thereof, wherein the arrangement comprises the steps of giving preferable density to both the upper layer and the lower layer of the nonwoven fabric with employment of adhesive bonding materials having preferable property and distributing a preferable amount of hydrophobic fibers and hydrophilic fibers to each layer, and a method of producing such nonwoven fabric.
Other objects of the present invention will become apparent from the following description.
The present invention provides an improvement in a nonwoven fabric and in a method of producing the same wherein: in a nonwoven fabric consisting of an upper layer having a substantially smooth surface and a lower layer having a density lower than that of the upper layer; the improvement which comprises a structure wherein said upper layer contains hydrophobic fibers of 80-100% by weight of its constitutional fibers, denier thereof being finer than in said lower layer, and containing a larger amount of adhesive bonding materials than in said lower layer; said lower layer contains hydrophilic fibers of 40-80% by weight of its constitutional fibers and hydrophobic fibers of 20-60% by weight of its constitutional fibers and these fibers are uniformly mixed, denier thereof being coaser than in said upper layer, and containing a smaller amount of adhesive bonding materials than in said upper layer.
The terms "upper layer" and "lower layer" used in the present invention do not indicate a state wherein thickness of a nonwoven fabric is equally divided into two but indicate a case wherein in a state of a plurality of fibrous webs formed through mixing of different fibers being overlapped to constitute a nonwoven fabric, such nonwoven fabric is divided into an upper layer having a relatively higher density and a lower layer having a relatively lower density. The term "density" means a case wherein the amount of fibers and adhesive bonding materials in each of the upper layer and the lower layer is averaged. The terms "containing amount of adhesive bonding materials" and "denier" mean a case wherein a containing amount of adhesive bonding materials and denier of the fibers in the upper layer and the lower layer are averaged.